In this research, variable wavelength photoelectron emission microscopy (PEEM) with tunable UV light from the Duke University free electron laser is applied to image single fibrinogen molecules adsorbed onto n -type silicon surfaces. High resolution PEEM images (∼10 nm) are obtained with photon energies from 4 to 6 eV. Wavelength-dependent image sequences are analyzed to determine the photoionization spectrum and the photoelectron emission threshold of individual molecules. The experimental data are fitted using temperature dependent Fowler law, square-root law, and cube-root law. The details of the theoretical models are discussed. The square-root and cube-root fittings reveal the ionization threshold of 5.0 eV for fibrinogen adsorbed onto n -type silicon, while temperature dependent Fowler law shows a threshold of 4.9 eV. The accuracy of the measurements is calculated to be ±0.2 eV. The authors conclude that no significant difference is observed from the three theoretical fitting approaches.
|Original language||English (US)|
|Number of pages||5|
|Journal||Journal of Vacuum Science and Technology B: Microelectronics and Nanometer Structures|
|State||Published - 2008|
ASJC Scopus subject areas
- Condensed Matter Physics
- Electrical and Electronic Engineering